1. Field of the Invention
The present invention relates in general to computer file systems, and more particularly to an extensible file access method for accessing a foreign file system from a data processing system with a native file system, said foreign file system and said native file system implementing different file system protocols.
2. Description of the Related Art
A file system comprises the logical structures and software function routines used to store, organize, and access information stored on a computer system's logical or physical storage media, such as a diskette, hard disk system, or optical storage. A variety of file systems have been developed to address various needs. For example, personal computer file systems comprise: File Allocation Table (FAT); Virtual FAT (VFAT); 32-Bit FAT (FAT32); New Technology File System (NTFS); and High Performance File System (HPFS). File systems for mid-range computers comprise: Unix File System (UFS), Network File System (NFS), and AS/400. Mainframe computer file system offerings comprise: Virtual Storage Access Method (VSAM); Sequential Access Method (SAM); Partitioned Data Set (PDS); and Object Access Method (OAM). File systems are not limited to these lists which are merely illustrative subsets of the numerous variety of file systems.
The various computer architectures and computer operating systems may use different file systems, thus organizing and accessing the information in different ways. Generally, these different file systems are incompatible, meaning that files created by one file system may not be accessed by another file system. A user may have a computer system supporting a particular file system, a native file system, and the user may wish to access and use information stored in a file system other than the native file system, a foreign file system. The user may need to access the foreign file system information for any of a number of motivations, such as to migrate the information to a replacement system, to archive the information, or to share the information among different systems.
Conventional systems have addressed this user need to access foreign file systems in a number of ways. The earliest conventional approach was to create a duplicate of the information and to convert the information in this duplicate from the native file system format to the foreign file system format. This approach is exemplified by patents such as U.S. Pat. No. 5,537,592, “System and Method for Reading and Writing Disks Formatted for an Operating System Foreign to the Host Computer;” U.S. Pat. No. 5,742,818, “Method and System of Converting Data from a Source File System to a Target File System;” Japan Patent Number 9231114A, “File System Conversion System;” and “Japan Patent Number 6243020A, “File Conversion Device.” U.S. Pat. No. 5,537,592 is representative of this approach, and in particular teaches a set of processes and data structures that allow transfer of user specified files between differently formatted disks. The processes identify the file format of the source and destination disks, retrieve the source files in the source file format, store the source files in a common format in memory that allows the directory hierarchy of the source disk and destination disk to be maintained, translate the contents of text source file records to the record format of the destination file system if desired, create directories and headers if necessary for the foreign disk for the transferred files, and store the files on the destination disk in a host file format. The user can then access and modify the files in the host file format using a host computer system. This approach is only a partial solution in that it only converts and reformats the information, it does not convert the software functions. The native file system can still only access information stored in the native file system format; it cannot access information stored in the foreign file system format, nor can it use the foreign file system software functions.
Another conventional solution is to install and support both file systems on the same computer system., effectively making the foreign file system an additional native file system. This solution is taught by U.S. Pat. No. 5,363,487, “Method and System for Dynamic Volume Tracking in an Installable File System,” which permits a single operating system to access a storage medium formatted in accordance with differing file systems. Generally, the operating system identifies which of a plurality of file system drivers is appropriate for reading a particular storage volume and, thereafter, associates the identified file system driver with the particular storage volume. Similarly, U.S. Pat. No. 5,911,776, “Automatic Format Conversion System and Publishing Methodology for Multi-user Network,” provides a set of multiple shadow file converters connected to a source file of an original document. Each shadow file converter enables the transformation of the original source file format into a particular other specific type of file format. However, providing all the permutations of the different types of file systems ported to the different types of operating systems and computer hardware architectures is probably not commercially feasible.
A more robust conventional approach is to directly convert file system requests from one file system protocol to another. For example, a client system, having a native file system protocol, may issue a request in the client's native file system protocol to a server. However, the server uses a foreign file system protocol which is different form the client's native file system protocol. A file system protocol converter translates the client's request from the client's native file system protocol to the server's foreign file system protocol. The file system converter may also convert the server response by reformatting the response's information from the server's foreign file system format to the client's native file system format. This type of direct file system protocol conversion is taught by: U.S. Pat. No. 5,218,697, “Method and System for Networking Computers Having Varying File Architectures;” U.S. Pat. No. 5,752,005, “Foreign File System Establishing Method which Uses a Native File System Virtual Device Driver;” U.S. Pat. No. 5,937,406, “File System Interface to a Database;” U.S. Pat. No. 5,864,853, “Portable File System Operable Under Various Computer Environments;” and U.S. Pat. No. 4,956,809, “Method for Canonical Ordering of Binary Data for Portable Operating Systems.” Foreign patents representative of this approach include: Japan Patent Number 10247155A, “File System Interface for Data Base;” Japan Patent Number 8137728A, “Portable File System and File Data Processing Method;” Japan Patent Number 7230396A, “Mutual Constitution System for Different Kinds of File System Forms;” and Japan Patent Number 10260877A, “Protocol Conversion System in Client Server System, Method Therefor and Recording Medium Programmed and Recorded with the Method.” Publications of this approach include: “File Interface for Migrating Applications to Enhanced Persistent Storage Platforms,” IBM Technical Disclosure Bulletin, June 1992, p. 182-183; “AS/400 OS/2 PC Support Shared Folders,” id., December 1989, p. 202-205; “Method to Manage the Mapping of Logical to Physical Record,” id., December 1995, p. 261-262; “Implicit Mapping of File Data,” id., April 1995, p. 523-524; and “OS/2 Logical File System,” id., May 1992, p. 370-371. Although this approach is a significant improvement over merely converting the information format, it still suffers from the disadvantage of even more permutations, where the permutations for each converter for a different pair of source and target file systems ported to the different types of operating systems and computer hardware architectures is also probably not commercially feasible.
Thus, there is a clearly felt need for a method, system and computer program product for providing an improved extensible file access method for accessing a foreign file system from a data processing system with a native file system, said foreign file system and said native file system implementing different file system protocols.